According to IAF MD 11 2019
2.2 Standard audit approach: To determine the audit time for an audit of an IMS covering two or more management system standards/specifications, e.g. A + B + C, the Certification Body shall: a) calculate the required audit time for each management system standard/specification separately (applying all relevant factors provided for by the relevant application documents and/or scheme rules for each standard, e.g., IAF MD 4, IAF MD5, ISO/TS 22003, ISO/IEC 27006); b) calculate the starting point T for the duration of the audit of the IMS by adding the sum of the individual parts (e.g. T = A + B + C);
In case the starting point T is already reduced up to 30%, based on IAF MD 5 2019, then the final reduction of an integrated system is 44% from the tables of the Annexes of IAF MD 5 2019 (44% comes from duple reduction: initial 30% and then another 20%). Is this calculation of the audit duration accepted?
September 2019
Yes. This could be an acceptable calculation (Since the integration is not a reason for the reduction in audit time according to IAF MD 5, an additional reduction can be done in IMS audit time according to IAF MD 11 due to integration). However, the primary requirement is for the CB to provide sufficient time for a complete and effective audit (ISO/IEC 17021-1: 9.1.4.1), and that this should be justified when a calculation is used (ref. 38.2).